Electrochemical Catalysis Of Supported Pd-based Nanocatalysts

At present,the Pt-based catalysts is widely used in Fuel Cells,but the Pt-based catalysts severely restricts the large-scale application and development of Fuel Cells due to its lack of reserves,susceptibility to CO intermediate toxicity and poor stability.Therefore,the development of green,cheap,efficient and highly stable electrocatalysts is one of the key factors for the rapid development and large-scale application of Fuel Cells.Pd has relatively abundant reserves,low cost,not easy corrosion,in alkaline medium shows excellent activity and stability,became the first selection of Pt catalysts replacement materials.Therefore,in this paper,a series of Ag@Pd/C and Au@Pd/C core-shell structure electrocatalysts were designed and synthesized by improved polyol method,and Pd/alk-MXene（Ti₃C₂）catalysts were synthesized by ionic liquid/water interface synthesis method.The structure and electrocatalytic performance of Pd/alk-MXene（Ti₃C₂）catalysts were studied in the following three aspects:（1）Homogeneous Ag₁₀@Pd_x/C and Pd/C nano catalysts were obtained by using the weak reducibility of polyols.The physical characterization of the catalyst showed that the structure of the Ag@Pd core-shell and its interfacial partial alloy caused lattice distortion and small particle size（9 nm）.The electrochemical characterization（Cyclic Voltammetry,Chronoelectric Current）of Ag₁₀@Pd_x/C and Pd/C catalysts were tested for ORR and EOR properties.The results showed that with the increase in the atomic ratio of Pd/Ag,the ORR activity was in a"linear"relationship of the metal ratio.The Ag₁₀@Pd₃/C catalyst showed the highest activity per unit masses（-0.10 V,3.4 times of Pd/C）.In the EOR test,the Ag₁₀@Pd_x/C catalysts showed enhanced catalytic activity compared with Pd/C catalyst,and with the decrease of the surface Pd ratio,the peak current per unit masses of Pd（i_p）showed A trend of exponential enhancement.For example,the i_pof Ag₁₀@Pd₁/C was 2.39 A/mg _Pd,11 times that of the mass activity of Pd/C(0.215 A/mg _Pd).The core-shell structures Ag₁₀@Pd_x/C catalyst shows good ORR and EOR properties.The Ag atom in the core has a larger atomic radius than Pd,which makes the d-band shift of Pd on the surface,which is conducive to the adsorption of ethanol on the surface and enhances its catalytic activity.During ORR,Ag surface adsorption may be beneficial to the reduction and desorption of oxides and intermediates.（2）The highly dispersed Au₁₀@Pd_x/C and Pd/C nanocatalyst were obtained by using the weak reducibility of polyols.The physical characterization of the catalyst showed that the core-shell structure of Au@Pd and its interface partial alloying caused more obvious lattice distortion,and the particle size（4 nm）was smaller than that of Ag₁₀@Pd_x/C.The electrochemical characterization techniques（Cyclic Voltammetry,Chronoelectric Current）were used to test the ORR and EOR properties of Au₁₀@Pd_x/C and Pd/C catalysts.the results showed that with the increase of Pd/Au atomic ratio,the ORR activity was in a"volcanic"relationship with the metal ratio,and the Au₁₀@Pd₂/C catalyst showed the highest activity per unit mass（-0.10 V,11 times of Pd/C）.In the EOR test,the activity of Au₁₀@Pd_x/C catalysts showed obvious enhancement compared with that of Pd/C catalyst,and with the decrease of the ratio of Pd on the surface,the peak current（i_p）of unit mass Pd showed A trend of exponential enhancement.For example,the i_pof Ag₁₀@Pd₁/C was 0.85 A/mg _Pd,7 times that of the mass activity of Pd/C(0.12 A/mg _Pd).The introduction of Au expands the lattice spacing of Pd,resulting in the d-band positive shift of Pd,which is conducive to the adsorption of ethanol on the surface and enhances its catalytic activity.In the process of oxygen reduction,Pd enrichment on the metal surface reduces the binding energy of Au-O,which is conducive to the reduction and desorption of oxides and intermediates,and is more conducive to the electrocatalysis of ORR.（3）By changing the type of carrier,Pd/alk-MXene（Ti₃C₂）catalyst was prepared exploratory by ILs/water interface synthesis method.Highly dispersed Pd/alk-MXene（Ti₃C₂）nanocatalyst was obtained by optimizing the synthesis conditions.Physical characterization of the catalyst showed that Pd/alk-mxene（Ti₃C₂）catalyst still maintained a thin layer structure similar to that of MXene,and the synthesized Pd NPs were evenly distributed and had a small particle size（4 nm）.